Initial Flutter/Dart port of SharedInbox

IMAP/SMTP email client with offline-first architecture:
sync engine writes to Drift (SQLite), UI reads reactively
from the local DB. enough_mail vendored under packages/.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

README.md

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+# SharedInbox [![License: MIT](https://img.shields.io/badge/License-MIT-blue.svg)](packages/enough_mail/LICENSE)
+
+IMAP/SMTP email client written in [Flutter](https://flutter.dev).
+
+Targets **Android, iOS, and Desktop** (Linux, macOS, Windows).  
+Supports **multiple accounts** — each synced independently via IMAP IDLE.
+
+## Design philosophy: offline-first
+
+```
+IMAP/SMTP server
+       ↓
+  AccountSyncManager  ←→  Drift (SQLite, local DB)
+                                   ↓
+                             UI (reads only from DB)
+```
+
+The UI never touches the network. The sync engine runs in the background and writes to a local Drift database. Screens observe reactive streams from that DB.
+
+## Key packages
+
+| Package | Role |
+|---|---|
+| `enough_mail` (vendored in `packages/`) | IMAP / SMTP / MIME |
+| `drift` | Local SQLite ORM |
+| `flutter_riverpod` | State management / DI |
+| `go_router` | Navigation |
+
+## Building
+
+```bash
+# Install dependencies and run code generation
+dart pub get
+dart run build_runner build --delete-conflicting-outputs
+
+# Run on desktop
+flutter run -d linux   # or macos / windows
+
+# Run on Android / iOS
+flutter run
+```
+
+## Vendored enough_mail
+
+`packages/enough_mail/` is a local copy of [enough_mail](https://github.com/Enough-Software/enough_mail) so it can be modified if needed. It is referenced via a `path:` dependency in `pubspec.yaml`.